This chapter focuses on just war theory as an approach to Shakespeare and war. It gives an overview of different theories of war and illustrates their significance in the Elizabethan historical context. This includes a discussion of the most important readings of Shakespeare as a realist or a pacifist and a subsequent analysis of Shakespeare’s use of just war theory. Drawing on a variety of examples, this chapter exemplifies what is considered a just cause, a right intention, or a legitimate authority in Shakespeare’s plays; the analysis shows who is presented as culpable or responsible and under which circumstances the relation between the cause and cost of a war must be considered out of balance. The author traces this line of argument along illustrative readings of 3 Henry VI, 2 Henry IV, Henry V, and Troilus and Cressida and suggests that just war theory may offer another perspective on Shakespeare and war.